The basic prior designs upon which the present invention is an improvement are represented by the present applicant's U.S. Pat. Nos. 3,076,532; 3,197,938; 3,328,928; and 3,636,670. Although each of these designs was an improvement over what had gone before, further experience has proved the need for improvement, especially in the areas of durability, flexibility, ease of installation and use and economy of manufacture.
It may be accepted that volleyball, when skillfully played, is one of the most rugged of net games, and the net and posts supporting the net are subjected to forces tending to tilt the posts in all directions. Consequently, and particularly in a situation where the erection of the net is to be portable, the ground anchors must be easy to install, they must be durable to withstand the forces arising during play and they must be flexible and capable of rapidly recovering their initial or normal status.
The most closely related of applicant's prior U.S. Patents are Nos. 3,636,670 and 3,328,928, each of which discloses generally a member in the form of a Z in which one part is a ground-penetrating helix, a second part is a leg adapted to overlie the ground and a third part is an upright (or nearly so) post-receiving part. In No. 3,328,928, the junction of the leg and helix is substantially a right angle, so that the leg, overlying the ground, has no pre-stress. In 3,636,670, although the junction of the leg and helix is less than 90.degree. and the ground-overlying leg inclines downwardly from the top of the helix to the ground, the purpose of the inclination is not to pre-stress the leg but to keep the top of the helix above ground. The absence of pre-stress is further shown by the built-in tilt of the post-receiving part; i.e., that part tilts toward the helix axis extended so that when the net is tensioned via the post carried by the post-supporting part the latter tends to be moved to a vertical position.
According to the present invention, and having resort to a specific embodiment by way of explanation, the ground-penetrating and post-receiving parts lie on parallel axes and the leg extends at angles of less than 90.degree. to each. The purpose of this design is to enable pre-stressing or loading of the leg as the anchor is screwed into the ground to its final position. That is to say, the helix is started vertically into the ground, with the leg and post-receiving part being used as a crank or handle, until the bottom of the leg at the junction thereof with the post-receiving part initially contacts the ground. This means that the top of the helix will still be somewhat above the ground and the leg will incline downwardly and away from this top part. The leg is then manually lifted (being flexible) and the anchor is cranked deeper into the ground until the leg lies flat on the ground. The leg is thus stressed or loaded and the initially vertical post-supporting part is caused to tilt toward the helix axis extended. Then, when net tension is applied to the post carried by the post-receiving part, the leg is further loaded or stressed, thus giving a greater net tension than was heretofore attainable.
Other advantages flowing from this construction are that the leg, lying flat-wise on the ground, presents a substantially horizontal torque member; i.e., the forces applied to the post in a plane normal to the leg rock or twist the leg about a horizontal rather than an inclined axis; the top of the helix, being flush with the ground, does not present an obstacle over which some person could trip; the pre-stressed leg more tightly grips the ground and further resists twisting of the anchor about the helix axis; the tighter grip of the ground by the leg eliminates the need for stabilizers and the like, as the enlarged lower end of the post-supporting part in No. 3,636,670 or the wings of No. 3,328,928.
Even when used as a tie-down -- i.e., without the post-receiving part -- the present design affords many advantages; e.g., elimination of high or above-ground obstacles and tighter leg-to-ground gripping action.